I knew a very similar case between South Brazil and Uruguay. They share the same street, divided in two exact halfs. But there, you may see a very interesting contrsat, since Uruguay people speaks Spanish and Brazilian people speaks portuguese. People from each border knows how to speak the neighbor language almost without any accent, and they also speaks a mix of them two...a very hilarious mixture called "Portuñol" (pronounce "portuniol"). These two cities are named Santana d Livramento (Brazil) and Rivera (Uruguay).